In general, a spot welding is a sort of resistance welding technology, which is a method of welding metal plates based on a resistance heat generated by, in a state in which two or three metal plates to be welded are stacked and arranged between a pair of welding tips, pressing the stacked metal plates with the pair of welding tips and applying a current across the welding tips.
This spot welding is also referred to as a point welding, and is widely used for a thin plate welding for its advantage over other methods, which includes a short welding time.
A spot welding gun for the spot welding includes a pair of welding tips facing each other, and welds the metal plates by using a high-temperature heat generated by, in a state in which the welding tips are respectively brought into contact with top and bottom surfaces of the stacked metal plates, applying a high current across the welding tips. In recent years, a welding robot is widely used to perform a welding operation in an automated manner, which includes a robot arm equipped with the spot welding gun.
However, such a spot welding gun can cause a setting error in settings of welding force of the welding tip, current intensity, alignment (straightness), end diameter, zero point of the welding tips, and the like when performing the welding operation, wearing or shape alteration of the welding tip due to a long welding operation, electrode damage due to contamination on the welding tip, and a welding defect including degradation of quality, degradation of strength, internal crack, and the like.
In a conventional system, to cope with the above-mentioned problems, the welding force of the welding tip, the current intensity, and the like are inspected before starting the welding operation using the spot welding gun, and an operator inspects the straightness in visual contact, the end diameter, and the zero point of the welding tip, existence of foreign matter on the welding tip, and the like before starting the welding operation.
However, the operator's visual inspection of the straightness, the end diameter, and the zero point of the welding tip, existence of foreign matter on the welding tip, and the like takes a considerable time and causes a problem of reliability in inspecting the items.
In recent years, as described in Korea Patent No. 1,385,922, an inspection apparatus has been developed, which automatically performs an inspection of the end of the welding tip by using a vision device or automatically inspects the alignment (straightness) of the welding tip by using a sensor.
However, such a welding tip inspection apparatus offers only a single inspection process in a single unit of inspection apparatus, which necessitates the spot welding gun to be moved to another inspection apparatus to perform the next inspection after each inspection process, causing a limit in reduction of the inspection operation. Further, in the case of the vision inspection, a noise is likely to be generated in an image due to exposure of the welding tip to external light, and hence not only the time for analyzing the image is increased but also the inspection efficiency is degraded.